Construction of Tricyclic Nitrogen Heterocycles by a Gold(I)-Catalyzed Cascade Cyclization of Allenynes and Application to Polycyclic π-Electron Systems

A novel approach to the direct construction of tricyclic nitrogen heterocycles based on gold-catalyzed cascade cyclization of aminoallenynes is described. The expected biscyclization reaction of hydroxyisobutyryl-protected aminoallenynes was efficiently promoted by a catalytic amount of BrettPhosAuNTf(2) in the presence of iPrOH to produce 1,2-dihydrobenzo[cd]indole derivatives in good yields. When the reaction was combined with Friedel-Crafts acylation or palladium-catalyzed N-arylation, the resulting tricyclic products were efficiently converted into nitrogen-containing polycyclic aromatic compounds (N-PACs) with highly conjugated pi-electron systems. A newly obtained hexacyclic indolium salt showed characteristic concentration-dependent absorption and emission properties.

Automated summary

A novel method based on gold-catalyzed cascade cyclization of aminoallenynes for the direct construction of tricyclic nitrogen heterocycles is described. Efficient synthesis of 1,2-dihydrobenzo[cd]indole derivatives was achieved by promoting the expected biscyclization reaction of hydroxyisobutyryl-protected aminoallenynes with a catalytic amount of BrettPhosAuNTf(2) in the presence of iPrOH. The resulting tricyclic products were further converted into nitrogen-containing polycyclic aromatic compounds (N-PACs) with highly conjugated pi-electron systems.